This invention relates to the preparation of nitrogen-containing, water-soluble polymers prepared from polyamines and a water-soluble piperazine/epihalohydrin prepolymer, and to their use as flocculants.
The condensation of epihalohydrins with piperazine is one which has been known for many years, and which has been carried out under a wide range of varying conditions. For example, U.K. Pat. Nos. 1,448,183 and 992,011 disclose methods in which epichlorohydrin is condensed with piperazine, in the presence of strong base, for example, KOH and NaOH, to produce various insoluble solids.
Similarly, U.S. Pat. No. 2,963,483 describes a method for the preparation of N-glycidylpiperazine, and a product prepared by polymerization thereof. The N-glycidylpiperazine is prepared by treatment of piperazine with epichlorohydrin, to produce an adduct of the formula ##STR1## and subsequent treatment of the adduct with a base, for example sodium hydroxide, potassium hydroxide, sodium or potassium alkoxide, calcium hydroxide, or an amine base, to eliminate HCl and thereby produce N-glycidylpiperazine. The addition of epichlorohydrin, and dehydrohalogenation are carried out at a temperature of from 0.degree. C. to 50.degree. C., and the resulting N-glycidylpiperazine is a crystalline solid, which can be separated, and polymerized by heating to make a rubbery polymer. However, the polymerization of N-glycidylpiperazine is very difficult to control, and in practice it is difficult or impossible to stop the polymerization at a point at which the polymer is not a solid, or at best a gel.
Great Britain Pat. No. 1,416,454 purports to disclose a method for the preparation of a water-soluble polymer by condensation of epichlorohydrin and piperazine, at a mole ratio of approximately 1:1, and in the presence of strong base (NaOH). However, the reaction there disclosed is notoriously difficult to control, and almost invariably results in the production of a solid or gelled product.
European Patent Application No. 0,033,104 and corresponding U.S. Pat. No. 4,328,142 disclose the preparation of a water-soluble polymeric cross-linking agent for polyamines from epichlorohydrin and piperazine to produce a flocculant. In this method, a complex two-stage reaction is required to produce the desired water-soluble prepolymer, the first stage of which is carried out in the presence of strong base (NaOH), and the result of the first stage is then acidified, before further epichlorohydrin is added at low pH, for the second stage. Control of this reaction is difficult and therefore relatively expensive, because of the complex pH requirements. Furthermore, the overall reaction for the production of the flocculant is a three-stage one, which is complicated to implement on an industrial scale.
In view of the aforementioned deficiencies of the prior art processes, an improved method for producing water-soluble polymer flocculants which eliminates one or more of such deficiencies would be highly desirable.